This invention relates generally to disk drive systems. More particularly, this invention relates to a method and apparatus for restarting an aborted write operation by reducing the amount of time to set laser power within a disk drive system.
Personal computers typically connect to an optical disk drive, such as a CD-ROM to read data from a compact disk. On the compact disk, data is stored in the form of pits and lands patterned in a radial track. The track is formed in one spiral line extending from the inner radius of the disk to the outer edge. A pit is a location on the disk where data has been recorded by creating a depression in the surface of the disk with respect to the lands. The lands are the areas between the pits in the tangential direction. The reflectivity of the pits is less than the reflectivity of the lands. To store audio or digital information, the lengths of the pits and lands are controlled according to a predefined encoding format.
When reading information from the disk, light from a laser beam is directed onto the track and the light beam is reflected back to a photo-sensor. Since the pits and lands have different reflectivity, the amount of reflected light changes at the transitions between the pits and the lands. In other words, the encoded pattern of the pits and lands modulates the reflected light beam. The photo-sensor receives the reflected light beam, and outputs a modulated signal, typically referred to as an RF signal, which is proportional to the energy of the light in the reflected light beam.
In FIG. 1, the relationship of the RF signal to the pits 36 and lands 38 is shown. A smaller pit 36 or land 38 decreases both the period and the amplitude of the RF signal. The RF signal in the pits 36 and lands 38 has opposite polarity.
One encoding format used in optical disk systems is eight-to-fourteen modulation (EFM). EFM reduces errors by minimizing the number of zero-to-one and one-to-zero transitions. In other words, small pits are avoided. A zero is indicated by no change in the energy of the reflected beam for at least two clock periods. A one is indicated by a change in the energy of the reflected light beam, that is, a pit edge. Applying the EFM encoding rules, a pit or land will have a length corresponding to an amount of time for at least three and up to eleven clock periods and the electronics will output a corresponding voltage waveform as shown in FIG. 1.
When reading data, the RF signal needs to be decoded into a serial digital data signal. In one circuit, to decode the analog RF signal, a comparator compares the RF signal to a reference voltage to generate a digital data signal.
To write data to a CD-Recordable (CD-R) or a CD-Rewritable (CD-RW) disk, power is supplied to the laser which heats and melts a portion of the disk surface to create the pits. The optimum amount of power to supply to the laser depends on the characteristics of the disk, the optics, the laser, the temperature and the recording speed. The amount of write power is determined for each combination of recorder and recording speed at the time of recording.
When writing data on recordable media, a problem known as xe2x80x9cbuffer-under-runxe2x80x9d may occur. Buffer-under-run occurs when the host computer is unable to supply data as rapidly as the data is being recorded onto the media by the recording device. When buffer-under-run occurs, the controller on the recording device indicates an error condition and the write process is aborted.
In hard disk drives, to recover from a buffer under-run, the head is positioned over the sector that was being written when the write aborted and the sector is rewritten. The data that was already written in the sector prior to the buffer under-run is recorded again.
In an optical disk, a buffer under-run almost always results in the interruption of the writing process in the middle of a record. When a buffer-under-run occurs, the writing process is aborted, and the data record remains partially recorded. Because a location on the optical media is typically written once, using conventional methods, it is not possible to re-start the aborted writing process to write the remaining data of the data record at the correct location with sufficient precision to allow the recorded data to be read without excessive errors. Therefore, the media becomes unusable and is discarded.
In view of the foregoing, it would be desirable to provide a method and apparatus to write the unwritten data resulting from an aborted write, starting at the location where the writing process was aborted, with sufficient precision to allow the recorded information to be read without producing excessive errors. As a result, media that would otherwise be discarded, becomes usable.
The invention includes a method of writing data on a disk. The method includes the step of writing a first subset of data on a disk such that an amount of write power to write the first subset of data is adjusted in a closed-loop operation. A write-power signal representing the amount of write power to write the first subset of data is measured. After a write interruption, such as from a buffer under-run, a second subset of the data is written on the disk in an open-loop operation using the measured write power so that the second subset of data is adjacent to the first subset of data. The open-loop operation has a much faster response time than the closed-loop operation, which allows the second subset of data to be recorded without a noticeable pause between the first and second subsets of data.
The invention also includes a circuit to write data on a disk. The circuit has a write head. A drive circuit provides power to the write head to write data on a disk. A feedback control loop is connected to the drive circuit. The feedback control loop includes a closed-loop feedback path to supply power to the drive circuit during a normal write operation, and an open-loop control to temporarily supply power to the drive circuit to initiate a write operation after suspension of a normal write operation.